The present invention relates to a circuit for controlling the application of battery power from a vehicle battery line to an electrical circuit upon detection of ignition noise on the battery line. In vehicle accessories, such as overhead consoles which house electrical components such as HomeLink.RTM. transmitters of the type disclosed in U.S. Pat. No. 5,583,485, it is desirable to power such devices only when the vehicle is in operation, which typically is accomplished by an ignition conductor which applies battery voltage to such conductors when the ignition switch is activated. The utilization of ignition conductors, however, requires that a separate line be extended from the ignition switch to the overhead console area of the vehicle, which is both costly and somewhat difficult. On the other hand, a battery conductor for allowing the manual activation of courtesy lights under any conditions is typically extended to the overhead console so that overhead lights can be employed with the ignition in an off position. Thus, there exists a battery conductor in the overhead console area, and it is desirable to use such conductor for other applications only when the ignition is on.
In the past, some electrical circuits have been provided to selectively provide operating power to such items as radar detectors and the like upon detection of ignition noise. Such prior art circuits, however, require that the circuit be built into the vehicle's alternator itself or directly associated with the engine computer. It is desired to provide a circuit which can be independently mounted remotely from the engine compartment of the vehicle and coupled to a vehicle battery supply line but provide operating power only when the vehicle engine is in operation. Such an application can, for example, be for back lighting of display panels in an overhead console, which back lighting is desired to be present whenever the vehicle is in operation so that the operator can see the various back lighted control switches or displays which may be associated with such electrical circuits as garage door opening transmitters, paging receivers, message centers and the like, which have back lighted control switches, both during day light and night time driving conditions. Further, it is desirable to have a system which accurately detects ignition noise to provide operating power only when the ignition is activated and not upon detection of other transient signals, as well as a system by which power, once applied, remains on until the ignition is turned off.